One of the architectures of choice in the current state of the art in modern communication transceivers is Zero Intermediate Frequency (Zero-IF) architecture. Several of the drawbacks of this architecture can be minimized when the voltage controlled oscillator (VCO) is running at a non-integer ratio of the input/output frequency. This in turn requires a non-integer frequency division. Two current prior art approaches to non-integer division circuits are (a) feed-forward (118, 114) and (b) regenerative (148, 144), as illustrated in FIGS. 1(a) and 1(b), respectively.
Both circuits have been in use for decades, but they are somewhat limited in their applications. The resulting division ratio at the output (124, 154) is
      N    ±    1    Nand
  M      M    ±    1  for the feed-forward and the regenerative versions, respectively. The only degree of freedom, other than the divider (118 or 148), is whether the upper sideband or the lower sideband of the mixing operation is selected (either by filtering or by implementing an image-rejection mixer). The feed-forward circuit (100) has been somewhat enhanced in prior art by adding another divider (186), as illustrated in FIG. 1(c). In fact, the configuration in FIG. 1(a) is the special case of the configuration in FIG. 1(c), where P=1. This additional degree of freedom improves the flexibility of the circuit, such that the resulting division ratio at output (184) becomes
            N      ±      P              N      ·      P        ;however, this circuit is limited to fractions less than one, as both N and P are positive integers.
In fact, many ratios cannot be reached at all with current designs, without cascading circuits, wasting both power and area. Another disadvantage of cascading circuits is the spurious low frequency emissions generated, that will require filtering.
One of the embodiments of the present invention avoids the drawbacks in prior art designs in the range of non-integer ratios achievable, and it avoids cascading circuit drawbacks, such as wasting power/area or generating low frequency spurious emission.